Newbie question - actions 'by' a certain date?

I just finished reading GTD and I've already blocked off 2 days to get started, but something's still bothering me: what about actions that need to get done by (but not necessarily ON) a certain date? An example is a paper that needs to be written: assume that all the research has been done, and the task of writing the paper remains. Let's say it will take approximately 12 hours to write, and it's due next Thursday.

How do I capture this? If I put a calendar item in for Thursday, it could be that I miss the deadline since I didn't allocate enough time. If I put it in my actions list, then I'm not guaranteed to get to it by the deadline.

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